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PRE-TREATMENT OF DAIRY WASTE WATER

USING BIOPOLYMERIC FLOCCULANT

EXTRACTED FROM ORANGE PEEL

Shabna Banu A.M.1, Meena John M.

2

1,2Department of Civil Engineering, Govt. Engineering College Trichur, (India)

ABSTRACT

Biopolymeric flocculants are attracting great research interests due to their biodegradable and nontoxic nature.

Pectin is a biopolymeric flocculant, which can be extracted from fruit wastes, and thus the fruit waste can be

reused. This study focuses on the suitability of pectin extracted from orange peel to treat dairy waste water.

Pectin was extracted from orange peel. Extraction performances of two solvents (ie isopropyl alcohol and

ethanol) were compared. Extraction from orange peel using isopropyl alcohol gave maximum pectin yield ie

39.01%. Detailed characterization of extracted pectin was carried out using FTIR analysis and SEM analysis.

FTIR analysis confirms the presence of hydroxyl groups and polygalacturonic acid in the pectin molecules. The

performance of pectin was evaluated by conducting coagulation-flocculation experiments using FeCl3 as

coagulant and extracted pectin as flocculant. Response surface methodology was carried out using Box Behnken

design to find the optimum pH, coagulant dosage and flocculant dosage to maximize COD removal, phosphate

removal, nitrate removal and turbidity removal. Optimum conditions were obtained as pH=4.00, coagulant

dosage=99.49 mg/L and flocculant dosage=10.59 mg/L. At the optimum conditions, COD removal, phosphate

removal, nitrate removal and turbidity removal were 48.32%, 69.46%, 62.29% and 99.91% respectively. Setting

characteristics of sludge was evaluated based on sludge volume index. SVI index was obtained above 250 mg/L.

Thus the sludge is having poor settling characteristics and high effluent turbidity.

Keywords: Box Behnken design, Coagulation-flocculation, Dairy waste water, Pectin, Response

surface methodology

I. INTRODUCTION

Rapid industrialization contributes to large quantity of waste water and its treatment is highly imperative.

Compared to other industrials sectors, the dairy industry uses a much greater amount of water for each ton of

product and produce large amount of waste water. Due to the high pollution load of waste water, the milk

processing industries discharging untreated or partially treated waste water causes serious environmental

problems, thus appropriate treatments are required. Reducing the waste water treatment cost is gaining

importance recently in view of environmental sustainability. Biological methods are usually used for the

treatment of dairy waste water due to its biodegradable nature. But these methods consumes large amount of

energy and also they are very complex. It necessitates the pretreatment of dairy waste water prior to biological

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treatment. Coagulation- flocculation methods can be used as an effective pretreatment method for dairy waste

water. Because these methods can remove COD, phosphate, nitrate etc from dairy waste water and thus reduces

the organic loading of the waste water.

Chemically synthesized flocculants are playing dominant role in waste water treatment due to their low cost. But

these flocculants have various limitations such as increased sludge production; non degradable nature and

causes a lot of environmental problems. Biopolymeric flocculants are attracting great research interests due to

their biodegradable and nontoxic nature. Since biopolymeric flocculants are free of secondary pollution, they

could be a potential replacement for toxic chemical synthetic flocculants. Pectin is a biopolymeric flocculant,

which can be extracted from different fruit wastes materials, and thus the fruit waste can be reused. It opens a

new path for the management of solid waste and reduces the effects of sanitary landfills.

The increase in the demand for a proper solid waste disposal sites and the effects of sanitary landfills makes a

problem in the management of solid waste. Food and organic waste from residential areas, commercial by-

products and institutional uses produce the highest amount of waste at 63.1%, 76.8%, and 40.6%, respectively,

as compared to mixed papers, mixed plastics, textiles, rubbers and leathers, yard wastes, glasses, ferrous,

aluminum, and other wastes. It causes several environmental concerns such as leachate and run off, odor,

vectors, and fires. Moreover, it is reported that only 1–2% of this waste is being recycled while the remainder is

taken to disposal sites [1]. Hence, it is important to recycle the organic waste such as fruit waste into useful

biopolymer flocculant.

This study investigates the effectiveness of orange peel to yield pectin using acid extraction method and

compares two extraction solvent. It also studies the effectiveness of pectin for the pre-treatment of dairy waste

water.

II. MATERIALS AND METHODS

2.1 Waste water sampling and preparation of synthetic waste water

The dairy waste water was collected from MILMA Dairy plant, Ramavarmapuram. The samples were tested for

different waste water characteristics as per the standard methods (standard methods for the examination of water

and waste water, 19th edition, 1995).

Synthetic waste water was used for the study. It was prepared based on the characteristics of collected dairy waste

water. The quantities of constituents were found out by trial and error method.

2.2 Extraction of biopolymeric flocculant (pectin)

Acid extraction method was used. Orange was peeled and washed with distilled water in order to remove dirt,

dust and the residues of the pesticide spray. The peels were cut into small pieces, then it was blanch with boiling

water for 5 minutes to inactivate enzyme. Then it was filtered by hands through two cheese cloths or muslin

cloths. Then it was dried in an air ventilated oven for 24 hrs and ground to fine powder passing through sieve of

size of 80 meshes and packed in airtight, moisture-proof bag at room temperature and ready to the extraction

process. Fig 1(b) shows the finely ground orange peel powder.

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Fig 1 (a) Orange peel (b) Orange peel powder

About 20 g peel powder was dissolved in 250 mL distilled water and pH was adjusted to 1.7 using 1N HCl. The

mixture was heated in water bath at 90ºC for 120 minutes. After 120 minutes, the mixture was cooled and was

filtered through nylon cloth.

Fig 2 (a) Peel water mixture (b) Water bath heating (c) Filtration The filtrate was precipitated with 95% ethanol.

The jelly pectin was filtered through whatmen No 1 filter paper and was washed with 95% ethanol. Then it was

dried in an oven at 35ºC. The pectin powder was then collected and the pectin yield was calculated [2].

Fig 3 (a) Precipitation with ethanol (b) Jelly orange pectin (c) Orange pectin

The same extraction procedure is repeated using isopropyl alcohol instead of ethanol and the corresponding

pectin yield was calculated.

2.3 Characterization of extracted pectin

Physical characteristics such as colour, solubility and gel forming ability were determined by visual

observations. Equivalent weight, Methoxyl content and Anhyrouronic acid content were determined by titration

with sodium hydroxide [3]. The degree of esterification was also determined by titration with NaOH [4]. Ash

content was determined by ashing at 60 ºC for 24 hours [5]. Moisture content was determined using an air oven

method [5]. The morphological characteristics of pectin were obtained by SEM analysis. FTIR was used to

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detect the chemical composition and functional groups present in the pectin. SEM and FTIR were analyzed from

Sophisticated lab, Cochin University of Science and Technology, Ernakulum.

2.4 Coagulation- flocculation experiments using extracted pectin

Jar test was used to study the coagulation- flocculation process. Fig 4 shows conventional jar test apparatus used

for studying the coagulation- flocculation process. Synthetic waste water was treated using coagulation

flocculation process. FeCl3 and orange pectin were used as coagulant and flocculant respectively.

Fig 4 Conventional jar test apparatus

The working volume for each sample was 1L. Desired pH was adjusted with 1M HCl or 1M NaOH. After

adjusting the pH, coagulant was added followed by rapid mixing at 150 rpm for 3 minutes to homogenize the

Fe3+

cation. Next, flocculant was added to the suspension at slow mixing, 30 rpm for 30 minutes. The

suspension was then allowed to stand for 30 minutes for settling purposes. COD, phosphate, nitrate and turbidity

of the supernatant solution were determined as per the procedures in standard methods. The corresponding

removal efficiencies were found out.

2.5 Optimization of parameters

Optimization of parameters such as pH, coagulant dosage and pectin dosage were done using RSM in

MINITAB software version 16. The ranges of these parameters were selected by doing random experimental

trials.

2.6 Determination of settling characteristics of sludge

Settling characteristics of sludge can be analyzed using sludge volume index (SVI). The sludge volume index

(SVI) is the volume in millilitres occupied by 1 g of a suspension after 30 min settling.

Real dairy waste water was treated using FeCl3 and orange pectin. One litre of treated sample was allowed to

settle for 30 minutes and then the supernatant was passed through a filter paper. The filter paper was dried and

weighed to find suspended solids concentration. Then SVI can be calculated using (1):

SVI =

III. RESULTS AND DISCUSSIONS

3.1 Synthetic waste water preparation

Table1 shows the quantities of chemicals required for the preparation of synthetic waste water, which are

obtained by trial and error method. Table2 shows the characteristics of real and synthetic waste water.

(1)

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Table 1 Quantities of chemicals required for the preparation of synthetic waste water

Chemicals Quantity (mg/L)

Glucose 180

Yeast 10

Milk powder 1500

Starch 30

Ammonium chloride 150

Dipottasium hydrogen phosphate 25

Potassium dihydrogen phosphate 18

Magnesium sulphate heptahydrate 100

Calcium carbonate 150

Sodium nitrate 50

Table 2 Characteristics of real and synthetic waste water

Parameter Concentration of real

waste water

Concentration of

synthetic waste water

BOD 3100 mg/L 2900 mg/L

COD 4300 mg/L 4000 mg/L

Nitrate 252.1169 mg/L 303.901 mg/L

Phosphate 95.18 mg/L 60.24 mg/L

pH 6.7 6.4

TDS 541 ppm 446 ppm

Turbidity 470 NTU 311 NTU

Conductivity 1.05 mS 1.08 S

3.2 Extraction

Table 3 shows the pectin yield obtained from orange peel using isopropyl alcohol and ethanol.

Table 3 Pectin yields from orange peel

Extraction solvent Pectin yield (%)

Ethanol 30.799

Isopropyl alcohol 39.01

Comparing the two extraction solvents (ethanol and isopropyl alcohol), isopropyl alcohol gives highest pectin

yield. Ethanol or isopropyl alcohol is added to the fruit extract, so as to increase the alcohol content. Due to the

dehydration effect of alcohol, pectin precipitates as fibrous mass. It is due to the insolubility of pectin in alcohol.

Since isopropyl alcohol is a secondary alcohol, its reactivity is greater than that of ethanol. Also, isopropyl

alcohol dissolves more oil than ethanol. This may be the reason for the higher pectin yield from the extraction

using isopropyl alcohol. Extraction from orange peel using isopropyl alcohol gives maximum pectin yield

(39.01%).

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3.3 Characterization

3.3.1 Physical characteristics

Physical characteristics of the extracted pectin include colour, solubility and gel forming ability. Table 4 shows

the physical characteristics of pectin extracted from orange peel.

Table 4 Physical characteristics of extracted pectin

Colour Brown

Solubility Not soluble in cold water.

Medium solubility in hot

water

Gelling property High

Colour of pectin is important as it indicate the purity of pectin. Pure form of pectin is usually light brown in

colour. Factors such as surface contamination, environmental factors, types of fruits used and human error

contribute to the changes in colour. Extracted pectin is dark brown in colour, which may be due to the presence

of impurities. Pectin is less soluble in cold water and soluble in hot water. Orange pectin has only medium

solubility in hot water. It may be due to the presence of impurities such as fibres in pineapple pectin. Pectin is a

polymer having high gelling property. Orange pectin has high gelling property.

3.3.2 Chemical charcteristics

Chemically, pectins are a mixture of complex polysaccharides, homogalacturonan being the main component.

This is a linear polymer made up of repeated units of α-(1-4)-linked D-galacturonic acid, to form a long

polygalacturonic chain. Pectin is capable of forming gels with sugars and acids under certain conditions. Gelling

mechanism of pectin depends on various properties. Table 5 shows the chemical characteristics of the pectin

extracted from orange peel.

Table 5: Chemical characteristics of pectin

Characteristics

Equivalent weight 1250.00

Methoxyl content (%) 9.67

Total anhydrouronic acid (%) 68.99

Degree of esterification (%) 58.33

Moisture content (%) 6.09

Ash content (%) 1.01

Equivalent weight of pectin is an indicator of its gelly-forming ability, with high molecular weight pectin having

better ability to form gels [6]. Equivalent weight of orange pectin is obtained as 1250.00, thus it is having higher

gelling properties. Methoxyl content is an important factor in controlling the setting time of pectin, the

sensitivity to polyvalent cations and their usefulness in the preparation of low solid gels and fibers. High

methoxyl pectin (methoxyl content greater than 7%) forms gels in the presence of high sugar concentration,

usually sucrose or fructose and at low pH; whereas low methoxyl pectins (less than 7.0%) can form gels with

lower concentrations of sugars [6]. Methoxyl content of extracted pectin was obtained as 9.67%, which is

greater than 7%. Hence extracted pectin can be considered as high methoxyl pectin and forms gels in the

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presence of high sugar concentration. Pectin, which is a partly esterified polygalacturonide, contains 10% or

more of organic materials composed of arabinose, galactose and other sugars. Anhydrouronic acid content

indicates the purity of extracted pectin. AUA content of less than 65% indicate impurities due to the presence of

proteins, starch and sugars in the precipitated pectin [6]. AUA content of extracted orange pectin was obtained

as 68.99%. It is greater than 65%, hence it does not contains significant amount of impurities such as proteins,

starch, sugar etc. Degree of esterification describes the rate of gel formation. Pectin having degree of

esterification greater than 72% can be classified as rapid set pectin and pectin having degree of esterification

between 58% and 65% can be classified as slow set pectin. DE of orange pectin was obtained as 58.33%. Thus

orange pectin can be considered as slow set pectin. Low moisture content is necessary for pectin for safe storage

as well as to inhibit the growth of microorganisms that can affect the quality due to the production of pectinase

enzymes. Moisture content of orange pectin was obtained as 6.09 %. Lower ash content is a criterion governing

the purity of pectin. Ash content of orange pectin was obtained as 1.01%.

3.3.3 SEM Analysis

Fig 5 shows the SEM image of extracted pectin powder. The structure was unique in shape, smooth and has

more wrinkles on the surface.

Fig 5 SEM image of extracted pectin

3.3.4 FTIR Analysis

FTIR spectra in the region between 4000-400 cm-1

identified the major chemical groups in the extracted pectin.

The spectral data obtained were analyzed by comparing the FTIR spectra with the major absorptions in the IR

spectra of peptic substances, which is shown in Table 6

Table 6 Band assignments of major absorptions in IR spectra of peptic substances

Frequency (cm-1

) Assignments

3600-3100 O-H stretching band (Acikgoz, 2010)

3000-2800 C-H stretching bands (Acikgoz, 2010)

1800-1200 Carboxylic groups (Acikgoz, 2010)

1750 Stretching C=O mode non-ionized methylated or protonated

carboxyl ionization (Acikgoz, 2010)

1650-1600 Asymmetrical stretching vibrations due to the COO– group of

polygalacturonic acid (Acikgoz, 2010)

1450-1400 Symmetrical stretching vibrations due to the COO– group of

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polygalacturonic acid (Acikgoz, 2010)

1200-1100 R-O-R or C-C bonds (Acikgoz, 2010)

1000-1104 Galacturonic acid (Acikgoz, 2010)

1070-1040 Carbohydrate backbone (Prabu and Natarajan, 2012)

Fig 6 shows the FTIR spectra of pectin extracted from orange peel. The peak centered at 3419 cm-1

indicates the

presence of OH–

groups. The peaks in the region 1230 cm-1

and 1745 cm-1

show the presence of many

carboxylic groups in the pectin molecules. A major band centered at 1647 cm-1

and a less intense band centered

at 1441 cm-1

respectively shows asymmetrical and symmetrical stretching vibrations due to the COO– group of

polygalacturonic acid. The absorbances at 1018 cm-1

, 1072 cm-1

and 1103 cm-1

show the presence of

galactoronic acid. The band centered at 1103 cm-1

and 1149 cm-1

may be due to R-O-R or C-C bonds in the

pectin molecules. The bands at 2856 cm-1

and 2926 cm-1

indicates C-H stretching bands.

Fig 6 FTIR spectra of pectin extracted from orange peel

3.4 Coagulation-flocculation treatment

Ranges of parameters such as pH, FeCl3 dosage and pectin dosage were determined by doing various initial

trials, which is shown in Table 7.

Table 7 Levels of parameters for the treatment using orange pectin

Parameter Low level High level

pH 4 8

FeCl3 dosage (mg/L) 50 150

Pectin dosage (mg/L) 10 15

Table 8 shows the removal of COD, phosphate, nitrate and turbidity corresponding to the experimental runs

obtained from the software.

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Table 8 Results of experimental runs

Run

order pH

FeCl3 dosage

(mg/L)

Pectin dosage

(mg/L)

COD

Removal (%)

Phosphate

removal (%)

Nitrate

removal (%)

Turbidity

removal (%)

1 6 100 12.5 35 66.67 56.623 83.900

2 6 50 15.0 9.5 6.98 51.810 96.141

3 6 150 15.0 30 44.44 61.440 99.680

4 4 100 15.0 20 26.67 56.623 98.714

5 8 100 15.0 20 22.22 18.670 49.196

6 8 100 10.0 30 53.33 10.840 66.560

7 6 100 12.5 35 66.67 56.623 83.900

8 4 50 12.5 40 62.22 51.810 96.784

9 8 150 12.5 20 66.67 38.759 35.048

10 6 150 10.0 30 83.33 61.440 97.106

11 8 50 12.5 20 15.55 10.840 33.440

12 6 100 12.5 35 66.67 56.623 83.900

13 4 150 12.5 35 44.44 80.720 91.320

14 6 50 10.0 30 55.55 54.220 97.120

15 4 100 10.0 50 66.67 61.446 99.680

The optimum values of the experimental parameters (pH, FeCl3 dosage and pectin dosage) for the

removal of COD, phosphate, nitrate and turbidity are obtained by RSM using Minitab Software, version 6.1.

Fig 7 Optimization plot

Figure 7 shows the optimization plot obtained from the software. The optimum conditions obtained from

Minitab are approximately pH=4.00, FeCl3 dosage=99.49 mg/L and pectin dosage=10.59 mg/L. At the optimum

conditions, COD removal, phosphate removal, nitrate removal and turbidity removal are 48.32%, 69.46%,

62.29% and 99.91% respectively.

pH is an important factor influencing the flocculating activity. Pectin gels in the presence of acids to form

hydrogen-bonding and hydrophobic interactions, which reduces the electrostatic repulsions. At low pH, the high

concentration of H+ causes formation of hydrogen-bonding and hydrophobic interactions. It leads to bridging

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mechanism during flocculation. Hence a lower pH is favorable for effective coagulation-flocculation process

(Chia et al, 2010). But there is an ideal range of pH for each of the coagulant. The pH range of FeCl3 is 4 to 11.

At a pH below 4, FeCl3 is not active. Hence a pH of 4.00 was obtained as optimum pH from the software. By

the coagulation flocculation process, dissolved materials can be precipitated and are removed by gravity. As a

result a clear supernatant is obtained. Due to the removal of dissolved materials, there will be considerable

removal of COD, phosphate, nitrate, turbidity etc.

Ferric chloride when added to water yields ferric and chloride ions. Ferric ions neutralize negatively charged

particles and leads to agglomerization of the particles or it may combine with hydroxide ions to form ferric

hydroxide which adsorbs particles, providing clarification of effluent. Low concentration of coagulant may

affect the charge neutralization process and results in reduction of flocculation activity. High concentration of

coagulant may lead to adverse effect where the surface of particle becomes positively charged. When this

phenomenon occurs, bridging of particle during flocculation is difficult. Therefore an optimum coagulant

dosage is required for effective flocculation (Chia et al, 2010). Hence a coagulant dosage of 99.49 mg/L was

obtained as optimum dosage.

Pectin is added to the waste water in order to carry out the flocculation process. The effectiveness of

flocculant adsorption depends on the amount of polymer adsorbed per unit area of the surface of the particles. At

low concentration of flocculants, the flocculating activity is low. This is because the particle surface is not ready

to induce any flocculation and very low adsorbent site is available for particle adhesion. At high flocculant

concentration, the coagulation–flocculation process is not complete. The surface of particle is insufficient for

polymer adsorption creating high competition among the flocculant. Hence an optimum concentration of

flocculant is required for the effective flocculation (Chia et al, 2010). Therefore an optimum pectin dosage of

10.59 mg/L was obtained from the software.

3.5 Settling characteristics of sludge

Spellman's Standard Handbook for Wastewater Operators gives the settling characteristics of sludge

corresponding to a particular SVI value. Table 9 shows the interpretation of SVI results, which are given by

spellman’s standard handbook.

Table 9 Interpretation of SVI results

SVI Range Expected condition

< 100mL/g Old sludge; possible pin floc; increasing effluent turbidity

100mL/g to 250mL/g Normal operation; good settling; low effluent turbidity

> 250mL/g Bulking sludge; poor settling; high effluent turbidity

The obtained SVI value is 625.00 mL/g, which is above 250 mg/L. Thus the sludge is having poor settling

characteristics and high effluent turbidity.

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IV. CONCLUSIONS

The study investigated the performance of biopolymeric flocculant (pectin) extracted from orange peel to treat

dairy waste water. Extraction performances of two solvents (ie isopropyl alcohol and ethanol) were compared.

The results revealed that Isopropyl alcohol is more effective for the extraction of pectin than ethanol. Extraction

from orange peel using isopropyl alcohol gave maximum pectin yield ie 39.01%. Chemical composition of

pectin was analyzed by using titrimetric method. The results revealed that orange pectin has higher gelling

properties. Extracted pectin can be considered as high methoxyl pectin and forms gels in the presence of high

sugar concentration. Detailed characterization of extracted pectin was carried out using FTIR analysis and SEM

analysis. FTIR analysis confirms the presence of hydroxyl groups and polygalacturonic acid in the pectin

molecules. The SEM image gave a smooth morphological topography of pectin molecules.

Synthetic dairy waste water was treated by coagulation-flocculation method using FeCl3 as coagulant and the

extracted pectin as flocculant. The effectiveness of orange pectin to treat dairy waste water was analyzed. The

results showed that orange pectin can be used for the pre-treatment of dairy waste water. It significantly reduces

COD, phosphate, nitrate and turbidity from the dairy waste water.

Response surface methodology was carried out using Box Behnken design to find the optimum pH, coagulant

dosage and flocculant dosage to maximize COD removal, phosphate removal, nitrate removal and turbidity

removal. It can create a set of experimental runs that reduce the number of runs needed to optimize the operating

conditions. The optimum conditions obtained from Minitab are approximately pH=4.00, FeCl3 dosage=99.49

mg/L and pectin dosage=10.59 mg/L. At the optimum conditions, COD removal, phosphate removal, nitrate

removal and turbidity removal are 48.32%, 69.46%, 62.29% and 99.91% respectively.

Real dairy waste water was treated under obtained optimum conditions of pH, coagulant dosage and pectin

dosage. Setting characteristics of sludge was evaluated based on Sludge volume index. The results revealed that

the sludge is having poor settling characteristics and high effluent turbidity.

V. ACKNOWLEDGMENT

The authors wish to thank the Govt. Engineering College, Trichur, Thrissur, Kerala where the study was

conducted.

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